Clitoral hood making a tent for the erect clitoris: sexual stimulation
causes arousal tumescenceand the clitoris
rises up and stretches its foreskin, left anterolateral view Stimulated
erect penis and neglected erect clitoris during penis in vagina penetrative sex (sexual intercourse or coitus)

In
the Global Survey of Sexual Attitudes and Behaviors (Laumann et al.,
2005), that used computer-assisted telephone interviewing and postal
questionnaires to assess sexual problems in 9000 women aged 40–80
years, the prevalence of “inability to reach orgasm” ranged from
17.7% (in Northern Europe) to 41.2% (in Southeast Asia). Kinsey et al.
(1953) found that 9% of women reported having been unable to ever
experience orgasm. Lloyd (2005), in her book on female orgasm, included
a table on orgasm rates during coitus obtained across a number of
studies; the percentage for women who reported “always” or “almost
always” experiencing orgasm during coitus ranged from 12% to
59%. J Bancroft a, CA Graham
The varied nature of women's sexuality: Unresolved issues and a
theoretical approach , Hormonal Behaviour. 2011 May;
59(5):717-29

Although
approximately 90% of women report orgasm from some form of
sexual
stimulation, most women do not routinely (and some never)
experience orgasm solely from sexual intercourse (Lloyd,
2005). By contrast, nearly 100% of men routinely
experience
orgasm solely from sexual intercourse. This gender disparity
in
the reliability of reaching orgasm during sexual intercourse
has
been thought to reflect evolutionary (Lloyd, 2005) or social
(Hite, 1976) processes. An anatomical explanation for this
disparity has also been proposed such that variation in the
distance between a woman's clitoral glans and her vagina predicts the
likelihood that she will experience orgasm in Q3 intercourse
(Narjani, 1924). Specifically it was proposed that if this
distance is less than 2.5 cm a woman is very likely to have
orgasms solely from sexual intercourse. This relationship has
not
been statistically evaluated, but two historical studies
provide
data supporting such a relationship (Narjani, 1924; Landis et
al.,
1940).
Data from two independent samples, collected over 70 years
ago and more than 15 years apart, support the notion that the
distance between a woman's clitoris and her vagina influences
the
likelihood that she will regularly experience orgasm solely from
intercourse. Women who reported more regularly experiencing
orgasm had shorter the clitoral-urinary meatus distance (CUMD)
measurements than did women who reported not experiencing or
less
regularly experiencing, orgasm in intercourse. When orgasms from
masturbation were considered there was no meaningful
relationship
between CUMD and whether or not a woman experienced
autosexual orgasms. Thus the influence of CUMD on women's
orgasms
is likely limited to orgasms solely from sexual intercourse.
These results suggest that some of the variability in women
experiencing orgasm from intercourse without concurrent
clitoral
stimulation reflects, as Bonaparte suggested in 1933, the consequences
of embryological processes that determine the position of the
clitoris relative to the vagina. Thus, some women may be
anatomically predisposed to experience orgasm from
intercourse,
while the genital anatomy of other women makes such orgasms
unlikely. While other factors, such as the sexual
characteristics
of a woman's partner, undoubtedly influence the likelihood of
experiencing orgasm solely from intercourse, these data
suggest
that for some women their genital anatomy strongly influences
the
occurrence of orgasm in intercourse. K Wallen, EA. Lloyd, Female sexual arousal: Genital
anatomy and orgasm in intercourse, Hormones and Behaviour. 2011 May;
59(5):780-92.

Prior
to first coitus, the clitoris is usually the only source of female
orgasm. It has the obligatory role of activation-establishment of the
epigenetic connection of the orgasmic circuit. If this neural reflex
circuit is not active during childhood it will never be functional. In
the months or years following first coition, intra-vaginal penetration
cannot trigger an orgasm unless this circuit is functional. Ablation of
the clitoris during the infancy prevents the establishment of the
reflex circuit, and the woman will never be able to experience clitoral
or vaginal pleasure. Gerard
Zwang:
Functional and erotic consequences of sexual mutilations, Presented at
the Fourth International Symposium on Sexual Mutilations, University of
Lausanne, Lausanne, Switzerland, August 9-11, 1996.

***

Orgasm
is a complex reflex. It encopasses numerous pathways and nervous
connections of such magnitude that one can speak of a vast orgasmic
circuit. At
birth this circuit only exists in a rudimentary state. Similarly, other
nervous circuits, such as that which controls bipedal locomotion and
that which regulates spoken language, exist in a rudimentary stage at
birth. The establishment of these circuits is epigenetic, that is,
secondary to birth, and dependson the full development of these
connections and the synapses connecting the neurons under the influence
of endogenous stimulation.